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What aerodynamic improvements were introduced on the Boeing 787?
When discussing the Boeing 787, three topics are brought up most often:

The new, extremely high-bypass GEnx engines
The shift to carbon composite construction and
The significant troubles Boeing encountered in manufacturing the airplane. One area I've seen less discussion is in the aerodynamic properties of the aircraft.

With that in mind, I'm curious whether Boeing made specific aerodynamic improvements to reduce drag and increase efficiency of the 787 relative to previous generation aircraft, and if so, what specific improvements were made. I recognize that it might be difficult to find this information given how recently the plane was created, but I thought I'd ask the community just in case!

Here is a quote from a former Boeing Technical Fellow for Aerodynamics that I got after emailing them about this very topic. I thought the community might be interested in his answer.

From the mid-90's to the mid-2000's, significant advances were made in
computer-based tools for closed-loop aero shape optimization,
Multi-Disciplinary-Optimization (MDO) tools for doing complex
multi-dimensional trade studies across scores of design variables,
structural Finite Element Analysis (FEA) optimization for structural
weight and stiffness. Much of this work was done as part of attempting
to meet the requirements of the HSCT (High Speed Civil Transport)
through its NASA-funded "HSR" element, and the follow-on industry
internal R&D efforts toward designing other "concept planes" like the
Sonic Cruiser, SSBJ concepts, and Blended-Wing-Body (BWB). The
supersonic airliner concepts and SSBJ in particular, required being
able to optimize not just the wing shape, but the wing, body, and
nacelle shapes simultaneously, optimizing to find the best possible
compromise between cruise aerodynamics, transonic acceleration,
subsonic cruise, and low-noise takeoff and landing performance. The
very thin, supersonic wings and tails, also provided significant
weight reduction, aeroelastics, and flutter challenges that acted as
catalysts for the improved structures tools. The MDO capability (still
evolving) helped make the right kinds of trade-offs, i.e. "optimum
compromises", in the design of the 787 and 777X. The improved CFD for
air-loads prediction were coupled with FEA strength and stiffness
optimization and these were used to guide direct optimization of
aerodynamic shapes.  The advent of practical direct CFD optimization
of detailed aerodynamic shapes for 787 enabled the computer to find
multiple incremental drag reductions that the "pressure matching"
methods used on the original 777 could not.  This optimization plus
the development of very strong carbon fiber primary wing structures
resulted in trade-offs that determined it was better to make the wing
thinner while using less sweep to get a fairly high cruise Mach of
0.85--- the resulting thinner all-carbon wing was plenty strong enough in bending, but was more flexible than previous wings.

It's not a total answer, and I wouldn't expect anyone from Boeing to give one, but nevertheless, it definitely confirms that a shift in design tools away from inverse design and towards direct lift/drag optimization led to incremental L/D gains.
I inquired a bit more about what specific flow features the optimizer was finding, and he said:

Very generally, yes, the computer-driven optimizations would seek ways
to improve L/D not just drag or drag-rise. So they don't really use
pressure distributions per-se as the figure of merit, rather the
actual L/D that results from various shape changes. This means that in
addition to trying to further reduce shock strength, they try to
incrementally raise the net difference between upper and lower surface
pressures thereby creating more "L" for a given "D". They also
distribute the lift span-wise in a patter than does not follow the
"ideal" elliptic lift distribution but rather try to create a
down-wash field that allows the horizontal tail and fuselage lift to
"trim" the airplane while minimizing the far down-stream wake. In a 2D
airfoil sense, carrying lift farther aft on the wing (both to increase
L and reduce shock strength) can cause thicker boundary layers,
increasing the parasite "form drag", but the thicker boundary layers
also have less local skin friction--- so the optimizer can seek the
best L/D trade-off of the various drag sources (wave/shock drag+skin
friction+span load induced drag+ tail and wake induced drag + wing
pressure form drag), and of course do this in the presence of the
nacelle and strut. It can also camber the nacelle and strut shapes,
change inlet lip shapes to reduce inlet drag, and put local "blisters"
or waves in wing surface, or change the shape of root fairings or wing
tips to get a better combination of local pressure and the local
surface slopes those pressures act on in the lift and drag directions
(very much a 3D effect !). You say you have trouble picturing what
would be advantageous for a full 3D optimization, but that is exactly
the point--- the computer can systematically do the grunt work to
investigate the effect of thousands of candidate shape variations,
identify which have the most performance leverage, and recommend
specific shaping trends that do not violate multi-disciplinary
constraints (spar thickness for example).

Anyways, hope the community appreciates. Not going to reveal the name of the Fellow, but can confirm privately if needed.

I can imagine Boeing designed specific airfoils for the 787 wing, optimized for the cruise at high mach number and for each wing section individually. Carbon fiber allows you to create a more complex shape than flat sheet metal so they probably had more freedom in designing that wing. Additionally it looks to me like they managed to reduce the number of rivets on the wing surface, reducing the drag further.
They also added cruise flaps which deflect the wing flaps down in cruise ever so slightly for ideal performance adjustments. Drooping the ailerons, flaperons and spoilers helps to reduce the drag in takeoff and landing configurations. Interestingly the idle glide ratio in clean configuration of the 787 isn't that much better than other aircraft if you look at idle descent planning manuals. It works out to be a glide ratio of about 1 to 22.5 or so, similar to the 777-300ER. I assume this is caused by the slightly increased wing sweep angle compared to the 777. The aspect ratio and the rest of the overall wing geometry looks quite similar to the 777, just scaled down. But increased sweep angle helps to increase the cruise Mach-number from 0.84 to 0.85.
Other aerodynamic improvements or changes: reshaped fuselage nose, streamlined cockpit windows, windshield wipers aligned with airflow, tail cone shape, laminar flow nacelle shape, new raked wing tip, horizontal stabilizer sweep angle increased, single slotted flap compared to double slotted flap on 777 (reducing complexity and weight, smaller flap track fairings), more takeoff flap settings on the 787-10 with adjusted slat schedule.
Others changes compared to 777-300ER: bleed-air-less system and Li-Ion batteries (reducing weight), no tail skid (reduces weight and complexity) increased window size, reduced cabin pressure altitude for increase passenger comfort.

I wonder if the airfoil sections you refer to were more advanced than the ones on the 777. As you can probably see from some of my other questions, I'm interested in the evolution of airfoil technology in the 1975-2010 period, and there was considerable progress from 1975 - early 1990s, where wings could be thicker and cruise at the same speed without incurring wave drag penalties. But post-777 , I wonder how much more gains there were to squeeze out of the airfoil.

Regarding the complex shape, it is something I wondered about too, but what exactly is "more complex" about the Boeing 787 wing shape relative to say, the 777? Is it something about the twist distribution?

The reason I ask by the way is because Boeing talked alot about how they deployed a new set of CFD tools on the 787 (see here: https://www.hpcuserforum.com/presentations/Germany/Boeing%20Ball%20IDC%20pdf.pdf) and that doing so made the wing "faster and
more efficient than previous aircraft". But that's not a lot to go on to understand how the new CFD tools helped.


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Why is a 3 degree descent angle used?
Following on from this question on the descent rate formula.
It appears from the answers and comments that a 3 degree slope is pretty standard across the board.
I would like to know why a 3 degree descent rate is used? I thought it would vary based upon the scenario.

Basically, it's a combination of historical significance, passenger comfort, and ease of mental calculation.
Historically, before aircraft were pressurized a rapid descent would be uncomfortable for passengers. At the speeds typically flown, a 300ft/min descent was deemed to be comfortable enough for the typical passenger.

Many aircraft had a cruising speed between 100–120 miles per hour (160–190 km/h). Three miles would be traveled in about 1.5–1.8 minutes, resulting in a rate of descent of about 550–660 feet per minute. That was about as fast as passengers could comfortably adapt to the changing pressure on their eardrums. However, many pilots used a 300-feet-per-minute descent rate because doing so is almost unnoticed by passengers. A pilot cruising at 10,500 feet would calculate that in order to be at 1,000 feet at his destination, he would have to descend 9,500 feet. Dividing 9,500 feet by 300 feet per minute, that descent would require about 32 minutes. If his ground speed was 120 miles per hour (190 km/h), he would begin his descent about 64 miles (103 km) from his destination (traffic permitting).

As you can see, there is a reasonably simple mental calculation that can be done there. This is commonly referred to as the rule of three which is in part quoted above.
That covers descent from cruising altitude, however you are right that flight in IFR will depend on procedures, and scenario. An example is London City Airport which uses a much steeper descent profile of 5.5 degrees on approach to land.

Three nanometers per 1000ft?!  Surely you mean n.m. ;)

@J... oh jokes based on SI. You dont get more pedantic than that ;) So as there is no SI unit for Nautical mile ive gone with the one used by ICAO according to https://en.wikipedia.org/wiki/Nautical_mile

I was stuck at NM also but nano is n not N and meter is m not M. After coming away with Newton Mega which does not scan I realized it was not an SI unit.  Since it was not expanded in full or linked I figured it must be well known to this community.  (Thanks to the popular network questions not having fikters you get a fair number of readers who are not among the community.)

I thought these were Newton-meters. Amittably not a very useful unit either.

I'm more stuck on the "at typical speeds" part. Is there any positive speed at which the ratio of vertical to horizontal distance traveled is not equal for a given angle? As far as nautical miles are concerned, I commonly see "nmi" used for it in order to help prevent confusion.

I don't see how this is speed dependent at all. atan((1000 ft)/(3 nautical miles)) is, in fact, about 3.14 degrees (a number which has nothing to do with pi). Speed comes in because the article you quoted mentions a descent rate of 300 feet per minute.

The descent angle used now has absolutely nothing to do with history and any other descent angle would be easily rounded to some other, but equally easily calculable, number.

Descent is a matter of managing the aircraft's energy budget.
To descend, the aircraft must shed all its potential, and big part of its kinetic energy. Pilots reduce engine power to minimum to stop adding energy, but the energy the plane already has is still only dissipated by drag. The angle at which the aircraft can descend without accelerating is equal to its lift-to-drag ratio. Descend any steeper and the aircraft will accelerate.
Now higher lift-to-drag ratio means lower fuel burn, so aircraft are designed to have that ratio high. A typical modern airliner has lift-to-drag ratio, at optimal speed, around 18. The older generation a bit less, 15-16, the newest aircraft a bit more, 20-21. And $18\times 1,000\ \mathrm{ft}\ \dot=\ 2.96\ \mathrm{NM}$.
The aircraft can descend less steeply by using some engine power, but the engines are less efficient at low altitude, so it is not desirable to descend slower.
The aircraft can also to some extent increase its drag, usually by using the speed brakes. However descending faster this way means that the engines were running longer before the descent started and thus burnt more fuel, the energy of which is now being wasted to speed brakes.
So pilots try to descent at around the optimal glide angle. And with the aerodynamics of current airliners it happens to be around 3 miles per 1,000 ft. Rounded to that value if you need to do the calculation mentally instead of having the FMS do it for you.

That would had been my answer, too. +1.

Jan, I think that the 3 deg was arrived at before FMS were standard fare.  (Heh, when I got my wings, my "FMS" was my brain and a wiz wheel).

@KorvinStarmast, of course it was. The lift-to-drag was a bit lower, but not that much, so that was already reasonable rounding down of the actual glide angle.

You already got my up vote, it's a nice concise answer.

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Airliner speed when descending through 10,000 feet
How do airliners get to 250 kts when descending through 10,000 feet as required by the FAA? Do you level off at 10,500 feet until speed is less than 250 and then descend further? Must pilots ask ATC permission to temporarily level off slightly above 10,000 feet to decelerate and then get further permission to continue descent? I’ve wondered for years how this works. On a 787 into SFO, we had the screens on the headrest that showed us GPS and speed etc. I remember looking at it on descent and noticing we were leveled off traveling around 145. Also, considering 250 is the maximum, do you travel around 240/245 above 10,000 feet to be sure you do not accelerate beyond 250? Thank you for the explanations.

Note that the speed you saw would have been ground speed not air speed. But in any case, you generally descend with the autopilot in a mode that pitches to hold an airspeed, called "Speed Mode" or something similar.  The other option is to descend in a mode that pitches to a vertical speed, called "VS" mode.  Speed  Mode is used most of the time.  You set the target speed the AP will maintain with a dial on the autopilot panel that moves a bug on the speed tape.
When you start a descent you will usually dial the speed you want to descend at, engage speed mode, then pull the thrust to idle, and over you go. Say you are descending with the bug at 290, which means the bug is set to 290 on the tape and the airplane will nose up or down as required to hold that speed, and in this case you are in some kind of dive.
As 10000 ft approaches, say passing through 12000, you just dial the bug down the speed tape to 250.  The airplane will pitch up a bit and start decelerating, then start pitching down again to maintain 250.  You try to time it so you are hitting 250 just as you are passing 10000.
ATC doesn't know your indicated airspeed, only your ground speed, so a controller has to estimate your airspeed based on the wind and ground speed.  This means being a few knots over the limit won't get you busted.
If you screw it up and are still too fast by more than say 10-20kt passing 10000 (or maybe because of some other imperative), then you'll dump some speed brakes to slow down faster.  But like I said, 10kts too fast passing 10 is not a big deal.

Great answer, but I'd like to point out that ATC actually can see your indicated airspeed, if the aircraft and the ATC facility are equipped to work with Enhanced Mode S transponders.
In fact, with this technology the ATC can even see the airspeed you have selected in your autopilot window. This is an extra layer of safety, so he can confirm you are complying with his clearance.

Thanks I suspected that.  My last IFR flight was some years ago.

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Why does the Dassault Falcon 7X's cockpit have ashtrays?
While looking at the first implementation of Fly-By-Wire systems, I see that the 7X was the first business jet with fly-by-wire controls.
Looking at the Wikipedia page for the aircraft, I saw this photo of the cockpit and noticed the ashtray in front of the sidestick on either side:

Why would there be an ashtray in the cockpit?
The Telegraph states that they are still present in aircraft toilets due to a FAA regulation that requires an ashtray be present in the event that a cigarette is lit and needs to be extinguished. However this doesn't cover the flight deck, surely the FAA doesn't assume a pilot will light-up during flight?

I don't think they are ash trays, probably just a convenient pocket for things like pens, cell phones, flash lights, whatever is in the pilots pockets...

@RonBeyer Well, for pens, flash lights, etc., I think I'd rather use that holder by the lower front corner of the side window (which seems to be occupied already on both sides). I'm not sure what they are, but I, too, doubt that they are ash trays. reidi2000, maybe this question would be better posed by [Edit]ing to instead ask what they are, and why they are there rather than why are there ash trays in the cockpit? What they are is probably answerable by referencing the POH; why they are there would likely require knowledge of aircraft design choices, unless obvious from function.

@MichaelKjörling Above the suspected ashtray there is an image of a cigarette being extinguished, similar to the image embossed on ashtrays in airplane toilets. This gives the impression that the intended use is not as earlier commented by Ron.

@reidi2000 Fair enough; I couldn't tell at first what that was supposed to depict (and didn't delve too deeply into it, to be honest). Now that you point it out, I agree.

To Ron's credit, the actual ashtrays aren't present in the picture. The placard is saying "put ashtray here".

Because Gauloises.

@user71659 got it right - the Dassault 7X has optional ashtray inserts that fit into those otherwise multi-use stowage pockets.

At first glance the two ramp workers looked like bobbleheads on the dashboard :D

@TomMcW That's because the plane is so big that it causes humans to look tiny. If the plane was of a more normal size, then surely the humans would appear much larger. :-)

@MichaelKjörling Lol! That little clip or whatever it is on the dash doesn't help. On my phone screen it makes the guy on the right look like a tiny action figure sitting with his legs hanging over the dash.

A lot of countries other than the US buy these planes. People smoke. I’m not grasping the mystery.

Amusing ashtray anecdote .. in 2013, was flying Air Transat VRA -> YYC-> YVR. After landing at YYC and waiting 20+ mins for them to open the cabin frozen door (-30C outside), they discovered the ashtray on the outside door of the front lavatory was missing. After a 15 min search,  They announced they would ground the plane for "missing safety equipment"! Much uproar ensued. After another 10-15 mins, I found it several rows away and over. We could "safely" depart! Canada was first country to ban smoking on airlines in 1989. The A321-200 model I was on launched development in 1995 (flew in '96).

In the United States, the smoking ban only applies universally to air carriers on scheduled flights. The regulation states

§252.4   Smoking ban: air carriers. Air carriers shall prohibit smoking on the following flights:
(a) Scheduled passenger flights.
(b) Nonscheduled passenger flights, except for the following flights
  where a flight attendant is not a required crewmember on the aircraft
  as determined by the Administrator of the Federal Aviation
  Administration:

(1) Single entity charters.
(2) On-demand services of air taxi operators.

(c) Nothing in this section shall be deemed to require air carriers to
  permit smoking aboard aircraft.

So for essentially all of the Falcon's missions, such as Part 91 corporate flights, and private charters under 10 passengers, smoking is permitted, as long as an "adequate number of self-contained, removable ashtrays" are provided (14 CFR 23.853(c)(1) or 25.853(f)).
Said ashtrays from a factory photo:

Closeup found here:

Correct answer, I know many private pilots (all over 60, TBH) that have the habit of "lighting one up" during the less stressful phase of the flight on their personal private airplane, mostly long finals glides on gliders....

In Europe and the US both AFAIK smoking in the workplace is not allowed. So unless you're flying your own aircraft and it's not owned by a company you wouldn't be allowed to smoke in it. This extends even to one man operations, a guy in England was fined for smoking in his van because it had corporate markings on it (he was self-employed), the same would go for aircraft.

@jwenting In the US, normal workplace rules, through OSHA, do not apply to aviation. Only FAA rules apply. (Along with train, truck, ship operators)

In general in the US, rules about smoking (except things like airplanes because "interstate travel" and other reasons) in the workplace, in various buildings, etc. are state or local regulations. There are few, if any, "nationwide" regulations for everyone when working. As a more recent example, mask rules vary widely by state/county/etc. and even in (at least most) places in the US where masks are required, if you are in a room by yourself you are not required to wear a mask. Similarly (though sometimes a bit more strict) if you are in a building of your own by yourself smoking is allowed.

Yes, there are no prohibitions on smoking in airplane cockpits.  Those are indeed ash trays.  Those of you who have traveled to Europe, especially France(!) where this airplane is made, will know that LOTS of people smoke and are free to smoke in many places that prohibit it in the U.S.

Mind providing a source?

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What is a possible reason for an L-1011 wing fuel tank overflow?
I was on a TWA Charter flight from Boston to Montego Bay Jamaica in 1989.  During pushback from the gate, the right wing began to leak jetfuel (like gallons pouring out of the wing).  They stopped the pushback and the first officer rushed back to take a look.  We didn't evacuate, the fire trucks came, and after the spill was cleaned up on the tarmac, we departed without incident.  Curious if this was a typical mishap on the L1011 or if someone could provide any possible reason for this to occur.  I couldn't believe we were allowed to depart without a detailed inspection.


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Are ASR and PAR approaches commonly used in Europe?
How common are ASR and PAR approaches these days? Are they still practiced anywhere in Europe?

Welcome to aviation.SE! I changed "SRA" to "ASR" because I believe that's the usual abbreviation but if it really should be SRA then of course please rollback my change or edit it again.

Yes, they exist. No, they are not common.


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Are there requirements for ice protection for general-aviation aircraft?
Does anyone know if any regulations exist making it a requirement for general aviation aircraft to have ice protection systems?
And any insights on why general aviation aircraft tend to use rubber boots and fluid based systems as opposed to electrothermal solutions?

welcome to aviation.SE. you ask about regulations. could you please specify the jurisdiction?

The UK or US, thank you

An airplane has to have a deicing or anti-icing system that is certified to a certain performance standard or it can't fly in icing conditions.  Icing conditions are defined nowadays as any visible moisture with temperature below a few degrees above freezing, so without a certificated anti-icing/deicing system the airplane is for practical purposes confined to below the freezing level if it has to fly through any cloud.
Boots/fluids are used because they only need compressed air or a reservoir/pump to work and take way less power to function vs leading edge heating systems that traditionally have depended on large amounts of bleed air (or electricity in the case of the 787) from a jet engine.  Even smaller jets like the early Cessna Citations could not produce enough bleed to anti-ice the wings and depend on boots.

Thank you very much


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What is fuel consumption of an A330 during climb and descent?
I want to know how to calculate or estimate an aircraft's fuel consumption when climbing from sea level to 15,000 ft, followed by a descent to 10,000 ft.
I would like to see an example for an Airbus A330-300 with CF6-80E1A4 engines.

This depends on the aircraft in question. Your specific aircraft should have performance tables that give fuel consumption figures, but without that, it would be a pretty wide estimate.

Hello and welcome to Aviation.SE. Unfortunately we cannot answer your question here because calculating fuel consumption is covered by an entire chapter in a ground school book. It is too much for us to cover.

One approximation could be done with the total energy, the specific energy density of the fuel and the engine efficiency.
(sum of kinetic and potential energy in J ) / ( J per kg fuel ) / ( efficiency ) = kg of fuel

Thank you for answer,  do you mean kinetic energy 0.5mv2, and potential energy mgh?

Descent tables
Climb tables
These tables are for the A330-200 and A330-300: in the footer of the page you can see for which engine these are. What you missed to indicate is the thrust setting, atmospheric conditions and weight to be able to give a realistic answer.

Thank for your answe. Sorry for late reply because i was not able to comment. What if Engine power is 304,7 kN each, maximum takeoff weight 233.000 kg while maximum landing weight 182.000 kg the data not enough? and for the tables where is the source If i want to get for another aircraft. Thanks

What do you mean? The climb tables are up to 240000 kg and the descent tables are 150000 or 200000: you can either round your weight or interpolate.


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How have engineers managed to increase commercial airliner wing aspect ratios over time?
Over time, the wing aspect ratios of commercial airliners have increased.
For evidence ,see the following data:

1980s:

Boeing 747-400: 7.91,
Boeing 757-200: 8.0
Boeing 767-300: 8.0
Airbus A310: 8.8

1990s:

Airbus A330: 10
Airbus A340: 9.2
Boeing 777: 9.96

2000s:

Boeing 787: 11

The advantage of a higher aspect ratio wing is that it increases L/D ratios by reducing induced drag, and thus for a given amount of lift, an airliner will incur less drag and burn less fuel. However, this is traded-off against the fact that the wing has to be thicker to counter the increased bending moments from the longer wings. This eats into the drag-reduction fuel savings.
But over time, it appears that engineers have managed to overcome the trade-off, making the wingspan longer without incurring the penalties of increased weight. How have they managed to do this?
Two notes:

On the most recent airliners (eg, the 787), there's considerable evidence that the shift to carbon composite wing structures has allowed for this to happen. However, the shift began before composite wing structures were introduced, so there must be other explanations
I'm almost sure Finite Element Modeling plays a role, but I'm just not sure how FEM allowed for the increase in AR without incurring the offsetting drag-increasing penalties.

It's much easier. Wing volume is driven by fuel needs. Aspect ratio is only the result of a chosen volume for a given wingspan.

A thicker wing allows more fuel to be stored in the wings, which reduces the amount that has to be stored in the fuselage, which helps offset some of that bending moment.

As to what makes higher aspect ratios feasible, no magic here:

Aerospace materials have improved over time, in quality and strength.

Carbon gets a lot of hype, part deserved and part not. It's just one of the materials.
Aluminum alloys range in yield strength from 55 MPa for the soft mush laptops and phones are made of to 650 MPa for structural aerospace parts. These are both common alloys currently in use. Steel has a further wider range.
Composites range in strength even more widely, from <100 to 3500 MPa, depending on the fiber, direction, weave, resin, filler, fiber ratio, and the curing method.
It's never just "aluminum" or "titanium" or "composite". Each is a very broad category. Overall, materials, including alloys, have been improving steadily; composites are most prominent at the latest step. Well before carbon, fiber-metal laminates have been cutting weight from the skin.

Better design precision.

Today's airplanes are engineered with CAD and FEA - finite element analysis. This allows for modeling the wing's structure in its entirety, down to small parts, and learning the stresses in each specific piece. Then, the pieces that are stressed less can be lightened, and the pieces that are likely points of failure can be reinforced.
The manufacturing methods have also improved, allowing for thinner layers, adhesive bonding, more precise milling and trimming. Overall, older airplanes had to carry a lot of metal that wasn't stressed as highly as it could have been, because it wasn't calculated accurately enough, or wasn't cost-effective to remove.
Today, it's common for airframes to come within a few percent of their calculated design load during destructive testing.

Larger airports.

Wingspan isn't just a matter of structural considerations. Larger wingspans have been feasible for a long time. The issue is, the wider it is, the fewer airports can fit the airplane in their gates, and the higher their landing fees. The FAA divides aircraft into design groups by wingspan, and airport design has to fit increasing requirements for each group.
The Boeing 747 and then the Airbus A380 have prompted airports to adapt to larger aircraft. Then, even as they are being phased out, the runways, the taxiways and the gates remain as designed for these "jumbo"/"superjumbo" categories.
This opens up room for slightly smaller aircraft like the A350 or the B777X to make use of these wider facilities. Since these planes are lighter than the 747 or the A380, they don't need as much chord to get the lift they need.

This is just the technical aspect. Keep in mind that higher aspect ratios were always possible, like used in gliders, but would always contribute more weight to the wing. There's a lot of reasons why higher aspect ratios were desired: increasing fuel prices, newer engines, more airframe stretching anticipated.

Thanks! Do you know about where I can learn more about materials development? Secondly, do you know if there's a good example of the types of dynamics that you're talking about with FEA - a case study for example that illustrates what you're talking about?

Answer: By having more efficient engines at their disposal.
Engineers had to choose lower aspect ratios than what they liked in the past. If you compare the reduction in aspect ratio which coincided with the switch to jets, you will see that larger aspect ratios were possible all along. Only the fuel-hungry early jets demanded a larger wing volume which was achieved by making wing chord larger than ideal. This helped to make flap systems less complex, but overall the aspect ratio was forced down below what would had been possible with more efficient piston engines.

Aspect ratio over year of introduction for different types. Blue dots = Piston engines, red dots = jet engines. More recent models could use more efficient engines and could get back to the higher aspect ratios of the piston era.
The How of a high aspect ratio wing is rather straightforward: Use thicker airfoils at the root and limit the permitted load factor and flight speed in gusty weather.

Thanks! Would it be possible to email you or DM you somewhere to ask you a couple of follow-up questions about the evolution of wing design over time in other areas?

@interested22 Why not ask them here so everyone can benefit?

Why did they increase fuel tankage by making the wings chordier, rather than by making them deeper?

@Vikki If with deeper you mean thicker (as in airfoil thickness): They wanted to fly fast so the jet would sell, and thicker wings mean earlier Mach drag onset. If you mean deeper as in increased wing chord: That should be the same.

@PeterKämpf: And supercritical airfoils (which make transonic mach drag a nonissue) hadn't been invented yet.

Further evidence that fuel-tankage needs were to blame: regional jets (such as the Caravelle and DC-9 in the 50s and 60s and the CRJs and E-Jets today) have less-chordy, higher-aspect-ratio wings than intercontinental jets, at the price of a shorter range due to reduced fuel capacity.

@interested22 ask a new question for each new topic. Share the knowledge with the community.


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How are the in-flight meals cooked?
When I traveled on a commercial aircraft, I had a meal which came in a small box, I was wondering if the meal is precooked and then re-heated or if it is cooked on the plane?

For the VtCs - this seems more operations related than passenger related (and therefore a better fit here than at Travel.SE, for example). We have other questions about in-flight item sales, aircraft turn-around procedures, and other not-directly-related-to-flight types of questions, this one seems fair game...

So really what you're asking is... What's the deal with airline food?

Airline food is usually prepared in ground and loaded on the aircraft, where it is reheated and served. In some cases, the food is half-prepared on ground and completed in air (in onboard ovens).
However, in some cases (Emirate Airlines, for example) business class customers can have (some type of) food prepared in-flight.

In general, food for commercial coach passengers is made on the ground and then stored on the plane in special refridgerators, until it is time to eat.
The food is then heated in convection ovens and served. Sometimes there are special occasions for higher class seats/airliners.

Safety standards and space constraints mean your food’s made on the ground, near the airport. Big boys like LSG Sky Chefs produce 15,000 bread rolls every hour (24hrs a day, 365 days/yr), and 30,000 sandwiches a day.
As a rule of thumb, food is prepared 10hrs before it gets eaten. Those “Made Fresh!” stickers are there to mock you. It’s not ready-to-eat by any means at this stage; generally, chicken is cooked 60% of the way, and steak 30% to done, with the final phase occurring onboard. Once cooked, it gets blast-chilled in special fridges -- in a not-quite-frozen-but-not-edible state, your food awaits transfer to the tarmac.
Flight on time? Food on the plane? Time to finish the prep-work. Contrary to what most people think, planes generally don’t have microwaves. Your little tray makes its way into a convection oven for about 20min. Convection ovens have a fan (which pushes hot air onto the food) that's both faster and means a lower cooking temp.

https://www.thrillist.com/travel/nation/airline-meals-how-your-airplane-food-is-made-thrillist-nation

What about for flights over 10 hours? how is food prepared then? Also, what about for non-coach? Does first class get something made on the plane?

From what I have read, food safety standards require that the food be made on the ground in special facilities that adhere to strict standards, unless the airliner signs a waiver. I would think this still applies for flights over 10 hours.

Some airlines will go all out and cook certain dishes on board in premium cabins (e.g. fresh eggs for breakfast on Austrian, even steaks cooked to order). In other cases, premium meals are made on the ground, but they may require more finishing touches by the flight crew (transferring items attractively to plates, tossing salads, pouring sauces, making ice cream sundaes to order, baking cookies, etc...)

@ZachLipton is it true in all of these cases where extra preparation/cooking is done by the flight crew, a waiver must be signed off beforehand?

@Prodnegel I've never had anyone cook me fresh eggs or a steak on a plane before so I can't speak to that. In the instances I've been in a premium cabin and a flight attendant has tossed a salad or fixed an ice cream sundae, nobody has ever asked about a waiver, nor have I ever heard of such a thing (nor can I find anything on Google). Assuming the food has been maintained at proper temperatures, why would it be more dangerous than food on the ground? It's possible that they use pasteurized eggs in such situations, and I'm sure all the ingredients come from a certified commercial kitchen.

@ZachLipton Sorry, I was wondering if the airliner had to sign a waiver to be able to prepare the food onboard. According to a site I can't find anymore, if food is not completely prepared prior to loading it onto the aircraft, then the airliner must sign a waiver.

@Prodnegel The airliner signs a waiver? I'm not sure what that means. It's certainly conceivable that the airline company would sign an agreement with the catering company acknowledging that the caterers aren't responsible if, say, an airline employee undercooks meat and a passenger gets sick (just as the butchershop isn't responsible if a land-based restaurant serves me undercooked chicken), but I wouldn't know anything about those legal arrangements between airlines and catering companies.

"Safety standards": whose standards? Does your quote apply to a country in particular?

Quite a few airlines have had celebrity chefs preparing food onboard certain routes before (not the top tier celebrities, but enough that some googling would give you something about them).  So long as the food is prepared to the standard of the land the airline is based in, there are no legal problems, its the same as cooking on a train or a boat.  I've had a decent rare steak and a soft fried egg on a BA flight in business before - both cooked to order.


text:
Which photo more accurately represents Flaps 1 in a 737-800?
A recent update in a sim craft changed the visuals from what I'm used to, but from my research it looks to be more realistic.
This picture depicting it being more extended:

or this picture depicting almost no flap movement:

This Aviation.SE post clearly reflects the more extended option being more realistic - but can anyone confirm that that is how it looks on a flaps 1 setting in real life?

What sim is this?

@RonBeyer probably x-plane if it's a stock 737 model

The bottom photo looks to me about like a clean wing (no flaps extended), while the top photo looks more like a Flaps 1 or Flaps 5 configuration.  Note that Flaps 1 is an uncommon takeoff setting in the 737-800 due to the increased risk of a tailstrike. Flaps 1 is common on the 737-700 on long runways, while the -800's and -900's generally use Flaps 5 or greater for takeoff.

Given the current state of the Zibo mod, you can assume the older version to be more accurate than the newer one. If you want one with the best flight model, you should not use one that's newer than the end of April 2018.

And which view do you as the pilot see when flying the simulator?

From a 737-800 today:
During takeoff, Flaps 5:

After initial flap retraction, to Flaps 1:

Conclusion: The first image in the question is a reasonable Flaps 1 depiction (more so than Flaps 5), and the second image is not a reasonable Flaps 1 depiction. It may not be a perfect Flaps Up depiction if there is the slightest misalignment in the trailing edges, but it certainly isn't a good depiction of Flaps 1.
Source: own photos.

It seems that you're right; but, respectfully, how do you know that this is a retraction from flaps 5 to 1 (instead of 10 to 5, or 5 to 2).

Because he was the pilot and is such a devoted contributor to ASE that he was running back and forth from the cockpit to the window to take pics--

I was deadheading on that flight, and it occurred to me right before takeoff to grab the photos for this exact thread. For the long runway being used, Flaps 5 is the only takeoff configuration our performance software would return. On flap retraction, there was the first retraction (to Flaps 1), the normal pause as acceleration happens, and then the retraction to the Flaps Up configuration. For a departure from a shorter runway, initial T/O flaps might be 10 or 15 or 25, and in a -700  aircraft then a Flaps 1  takeoff would be possible, but this was a Flaps 5 takeoff.

As to the Flaps 2 part of the question, we don't use Flaps 2 for takeoff (although the -200's could, and perhaps the -300's -- not certain about the latter) in the NG fleet. It's also not a stop on the retraction schedule - having started at Flaps 5 (or gotten there from a higher flap setting, 10 > 5, 15 > 5, 25 > 15 > 5), the next steps are to Flaps 1 and then to Up. Since I was deadheading on my own airline, I'm familiar with the procedures & flap retraction schedule being used.

Thanks for the clarification :)

On the 737, flaps 1 actually means leading edge slats only and no trailing edge flaps.
Therefore the first photo is definitely wrong, while the second one is probably correct (since the slats cannot be seen).

This is incorrect. Selecting Flaps 1 on a 737 does indeed extended the trailing edge flaps.

This answer is absolutely wrong. The TE flaps do extend at Flaps 1 on a 737.

1 is the answer to this question:
and

they are both the same

How do you know that’s flaps 1?

@MD88Fan The question is, which one more accurately shows Flaps 1. The picture with zero trailing edge flap extension is absolutely the WRONG answer. Even if the first picture shows, say, a Flaps 2 extension, it's still more accurate than the other.

The other two answers are wrong; this answer is correct.

Hey @hieverybody, welcome to Aviation.SE! please look carefully - the flap angle is different in both images. Even if it was the same, I do not see how it implies that 1 is the correct answer...

@AdityaSharma The question is either/or... which photo is a better depiction of Flaps 1.  Your own post shows that the second graphic in the OP is a nearly exact depiction of Flaps Up.

I am not sure about 737-8, but for 777 flap 1 only slats move.

Very good find! Could you add the source though?

This photo is from my ground school material, I only have texture version which from our company B777 FCOM.

This is not true for the 737. See e.g. here, flap position 1 moves the TE flaps.

Yeah, this is 777.... hahaha

This doesn't attempt to answer the stated (737) question, and the statement presented suggests the wrong answer. It might be better to edit or delete this answer.


text:
Where can I find the aerofoil geometry of a commercial aircraft so as to design it in CAD software?
As a part of my final year thesis, I need to design a commercial aerofoil for an existing aircraft (such as Boeing/Airbus) to conduct some FEA & CFD analysis. I've been trying to source aerofoil geometry so as to design it on CAD tools, but I haven't had any luck yet.
Note: I've gone through airfoiltools.com and I was looking for more than just the NACA Airfoil. I was hoping I could get the complete airfoil geometry including that of the spars, ribs, skin, slats, ailerons, spoilers & tanks. I've even tried going through the TCDS Database, but I haven't found any relevant information there.

Is your assignment to design an aerofoil, or to draw an existing one? You shouldn't need any existing aerofoil info to design a new one, especially for a school project.

All the current manufacturers develop proprietary airfoils combined with wing planform, washout, etc. using CFD for optimum pressure distribution, low drag, high critical Mach number, high maximum CL, benign stall propagation and benign aeroelastic characteristics. That applies to Boeing, Bombardier, Embraer and Airbus.
This type of info is not normally released by the manufacturers.
TCDS's do not have this kind of data.
You can do your own research starting with a standard NACA airfoils like those found in NACA report 640(Summary of Airfoil Data) and modifying them.

Also modern wings generally don't have a set airfoil shape, they are continuously varied from root to tip. Older wings may have set of airfoil shapes each placed at stations along the span and connected by basic geometries. (shapes suitable for real world materials used in manufacturing)


text:
Why do airliners pitch up during cruise?
In my experience as a passenger, when the plane stands at the airport and you enter it, the aisle is pretty much horizontal. (Obviously, I've never flown on a DC-3). After takeoff we pitch sharply upwards (duh!), but even after the captain comes on the PA with "we have now reached our cruise altitude", the aisle continues to point a few degrees upward. Usually it's only at "we're starting our descent into XYZ" that the body returns to a more or less horizontal pitch.
Why is this? I have some hypotheses, but don't know which, if any, of them hold truth.

It's just how the aerodynamics happen to work out. (Unlikely -- it would seem to be a simple engineering matter to attach the wings to the body at an angle such that the right angle of attack for cruise flight corresponded to the body being horizontal).
Pitching the body upwards slightly allows it to generate some lift, free of a proportional increase in drag relative to pushing the cylindrical body straight through the air.
Passenger jets are deliberately designed such that they never need to pitch lower than horizontal in a routine descent, lest passengers might panic and think they're nosediving to their death. (Also unlikely, unless there is really no hidden costs in terms of drag, etc.)
Landings might be more difficult if the plane had to point its nose downwards in order to get closer to the ground -- the nosewheel would hit the runway first. (On the other hand, simply leveling out would count as a flare, so it's not clear to me that's actually a disadvantage).

Lift from the fuselage being angled upwards is not "free of drag". All lift causes drag because no system is 100% efficient.

@DavidRicherby: My intention was "free of additional drag (to first order)". You can't have lift without drag, but you can certainly have drag without lift -- that's what you get for a symmetric fuselage at 0° angle of attack. If you pitch it slightly to give a small angle of attack, you're converting some of the drag-without-lift to drag-with-lift.

I'm very sceptical of that claim: it sounds too much like a free lunch. If you're arguing that the extra drag from pitching the nose up a couple of degrees is negligible, that suggests that the extra lift is negligible, too.

@DavidRicherby: Qualitatively, the additional drag is positive no matter whether you pitch slightly up or slightly down, so to a first approximation it goes as the square of the pitch angle. On the other hand, lift has opposite signs for opposite pitches, so I would expect that to be linear in the pitch angle (again to a first approximation). Therefore, for small enough pitch deviations from 0°, the change in lift will dominate the change in drag.

@HenningMakholm: When there is negative lift, more positive lift is needed and that induces more drag. That's why given angle down is worse than the same angle up. The rest is about the fact, that the resulting attitude depends on weight and in airliners that can make a big difference.

@JanHudec: That sounds like you're agreeing that my suggestion (2) is sane -- i.e. that a slight upwards pitch could be the most economic compromise between body lift and body drag. Right?

@HenningMakholm: Yes, I do. Plus the twist with the weight (see the full answer below).

A very well-written and interesting question; I'm sorry most of the answers so far are not up to a similar quality.  The core of the question seems to be: "Why do designers choose to require pitch-up in flight rather than choosing the wing incidence angle so the wings have the right angle of attack with zero pitch?"

Is this a real thing?  I always assumed this was an optical illusion caused by the lack of a static reference frame.

I'm not sure that your observation is correct.  I have always felt the fuselage to be roughly level in flight.  Next time you fly try momentarily setting your drink on the deck and see if it actually is tilted.  (to remove any compensating tilt of the seatback tray...)

Mainly the options 2 and 1 from your list.
What nobody mentioned so far, but is rather important here is that the angle of attack depends on speed1 and weight. While the "speed" does not vary much for most airliners, the difference between empty and fully loaded airliner is rather large.
Now if the fuselage was tilted down, it would generate lift directed down and associated drag with the net result of simply a lot of extra drag. So the aircraft is designed so that it does not fly (in level cruise) pitched down even when light. But that means that when it is fully loaded, it flies slightly pitched up, because it needs more lift and higher angle of attack to get it.
1 It depends on the "indicated speed", which is not speed at all but rather dynamic pressure expressed as speed at which it would occur when moving through air of standard sea level pressure (1013.25 hPa). The pressure at high altitudes where airliners normally fly is significantly lower, so the indicated speed is usually does not exceed 250 knots when true speed is well over 400 knots.

Lift from the fuselage helps to fill the gap between the wings and from wing sweep (Mitteneffekt). This will reduce induced drag; ideally the gap is completely filled.

Ultimately the answer to your question is number (1) from your options above - That's just how the aerodynamics happen to work out.
To generate a certain amount of lift requires that the wing have a specific angle of attack at a given speed. As the wings are more-or-less permanently attached to the fuselage setting the angle of attack requires us to pitch the entire aircraft, changing the deck angle.
There is a very nice web page illustrating this in (greatly exaggerated) detail, so I won't reproduce the full explanation & drawings here.

As to why the aerodynamics work out that way - that probably has something to do with numbers (3) and (4) - passenger comfort, and ease of executing maneuvers (like landings).
Most airliners I've been on have a slight nose-up deck angle (maybe 2 degrees) in cruise, which isn't really "noticeable" to most people unless you're carrying a bubble-level or staring very intently at your drink, but the exact angle for climb, cruise, and descent will vary depending on the aircraft and how it's been loaded (you can pretty much descend with any deck angle you like).
Most people would probably object to flying around with a 10 or 15 degree deck angle (whether nose-up or nose-down), so as a concession to passenger comfort the wings are attached to the fuselage in a way that is aerodynamically favorable (not trying to drag the fat bottom-side of the plane through the sky) and comfortable for the passengers.
Conversely most GA aircraft I've been in seem to cruise with a flat or slightly nose-down deck angle, though that could just as easily be an optical illusion from having the big window in front where you can see it. (I'm estimating the deck angle based on the wet compass tilt since I generally don't serve drinks.)

A deck angle of 2 degrees on a 200ft (60m) long plane corresponds to a 7ft (2m) height difference between the front and the back. I don't think you'd need a bubble level to see that.

It's not an optical illusion, many GA planes cruise with a slightly nose down pitch, sometimes referred to as flying "on the step". As I recall, the wing chord is pitched slightly upwards on most GA aircraft to generate more lift at a nose level pitch. That last part may be off slightly, going from memory. Source: As the Pro Flies

@DavidRicherby From the outside of the aircraft it's certainly obvious the deck is not level - you can see there is a difference between the nose and the tail. From the inside however a 2-degree inclination is somewhat less obvious. Observe the contents of a drinking glass the next time you're on an airliner - the liquid will probably be tilted, but it won't be a significant amount (i.e. "You're not substantially more likely to spill it on your tie").

@voretaq7: When you sit at the back and look forward the way you think it's level, you'll see the incline quite clearly. You won't notice it on the drink in a glass as that is too small; and the table might add incline of it's own anyway.

@voretaq7 Just look at the floor: it's going to be obvious if the floor is sloping up by about one foot (30cm) for every thirty feet (10m) of cabin length.

Perhaps I shouldn't have proposed option (1), since it answers a different (and less ultimate) question from the other ones. Obviously, once the aircraft is built, level flight in such-and-such conditions (speed, air pressure, weight, etc) will require a particular attitude, and if that happens to have the fuselage pointing upwards, then that's it. The other hypotheses are attempts to answer why the aircraft was designed such that the body points slightly upwards in typical cruise flight conditions.

Worth noting that the A330 has a pronounced nose-down angle when sitting on the tarmac. This gives it a more level cabin attitude in flight, but has posed serious issues with cargo handling - the A330F has redesigned nose gear specifically because of this issue.

You actually have some pretty good hypothesis here!
To start with, it truly is "a simple engineering matter to attach the wings to the body at an angle such that the right angle of attack for cruise flight corresponded to the body being horizontal", but you missed the design goals slightly.  This angle is called the angle of incidence, or the rigging angle of the wing and is the difference between the fuselage angle and the wing angle.  This is a very specific angle that is calculated as part of the design of the aircraft.

The wing incidence must satisfy the following design requirements:

The wing must be able to generate the desired lift coefficient during cruising flight.
The wing must produce minimum drag during cruising flight.
The wing setting angle must be such that the wing angle of attack could be safely varied (in fact increased) during take-off operation.
The wing setting angle must be such that the fuselage generates minimum drag during  cruising flight (i.e. the fuselage angle of
  attack must be zero in cruise).

These design requirements naturally
  match with the wing airfoil angle of attack  corresponding to the
  airfoil ideal lift coefficient (see figure 5.26).
The typical number for wing incidence for majority of aircraft is
  between 0 to 4 degrees.  As a general guidance, the wing setting angle
  in supersonic fighters, is between 0 to 1 degrees; in GA aircraft,
  between 2 to 4 degrees; and in jet transport aircraft is between 3 to
  5 degrees.

Notice that the proper angle of incidence will have the wing at its most efficient during cruise while the fuselage also generates the minimum amount of drag.  Both of these are calculated independently and the angle of incidence is set so that both conditions are satisfied at the same time.
Aircraft design decisions are usually a compromise between different, many times conflicting goals.  He goes on to say that it may be adjusted from the optimum in some cases:

The wing setting angle may be modified as the design process
  progresses. For instance, a  fuselage with large unsweep over the rear
  portion to accept aft cargo doors may have their minimum drag at a
  small positive angle of attack. In such cases, the wing incidence will
  be reduced accordingly. Another, les fundamental, consideration is
  that stopping performance during landing operation to get as much
  weight on the braked wheels as possible. Thus, there is a benefit to
  reduce the wing incidence slightly to the extent that the change is
  not felt significantly in the cabin. Reducing the nose gear length
  will do the same thing. This technique is limited in passenger
  aircraft because a level cabin floor is desirable on the ground. But,
  for fighter aircraft, the level floor is not a design consideration.

Another possible reason to adjust the angle of incidence to a non-optimum number is to ensure that when landing the aircraft the nose is not pitched down, in order to avoid a higher likelihood of hitting the nosewheel first on landing.

Most of the material for this answer came from this document written by Mohammad Sadraey at Daniel Webster College

This seems to be a better answer than the one selected, pointing to the minimum drag airspeed and the angle of incidence. I found another good explanation here.

You need a slight pitch-up attitude to fly: you need a certain angle of attack in order to produce the required lift to remain airborne.
As you have imagined, usually the wings are tilted with respect to the fuselage so that in cruise the wings will have the required AoA while the fuselage will be horizontal to minimize drag (and thus fuel consumption).
Passenger comfort is much less important than this (and passengers can always lean back their seats).
My hypothesis for your observation is that the "pitch-up" you observe is either a visual/sensory illusion due to the lack of external point of reference (no, the clouds are not a valid reference and the ground is too far away) or you have flown in aircrafts where the floor is not parallel to the aircraft x-y plane.
Personally, I would lean towards the first hypothesis, as having a non-horizontal floor in flight creates all kind of nuisances to cabin service (again, something you want to avoid).

You do not need a slight pitch up attitude to fly.  Ever seen a stunt plane?  The only angle that matters is the angle of attack between the chord of the wing and the relative airflow.  It is possible to design, and fly, aircraft which cruise nose down, nose level or nose up.

@Simon, ok maybe I have not phrased it in the best way, but if you notice I say what you point out: you can build/mount the wings with an angle w.r.t. the fuselage, so that this will have no pitch while the wings will have a positive AoA

Note that even 2 degrees of pitch up would cause the front end of a 200ft (60m) aircraft such as a 777 to be about 7ft (2m) higher than the back. That could very well be noticeable to the passengers.

Anecdotally, I was on a flight on Sunday and watched a cherry tomato roll down the aisle towards the back of the plane, seemingly due to the plane being pitched slightly upward.

@DavidRicherby: as you say in a comment to another answer, if 2° were so important, they would just pitch the seats by default (and they do) rather than increase the drag

@dimo414: exactly; "anecdotally", you cannot say that the only cause for it to roll to the back was a normal and clear flight attitude and you cannot extrapolate that it would be valid for all aircrafts

@dimo414 The tomato roll could have been caused by the plane accelerating. It wouldn't need to be accelerating very much at all.

@Federico your answer is the best.   Even the aerospace engineer said the same thing regarding about slight pitch up here:
http://sg.answers.yahoo.com/question/index?qid=20110821181822AA10BYO
http://science.howstuffworks.com/transport/flight/modern/airplanes.htm/printable

@Federico sure!! :-).

Every jet that I've ever flown has a nose up pitch of about 3-4 degrees during cruise, so I don't think that it is an illusion.  The floor actually is typically pitched up a little bit during cruise!  The rest of your answer is spot on though.

This answer seems inconsistent with itself. "You need a slight pitch-up attitude" but "the wings are tilted with respect to the fuselage so ... the fuselage will be horizontal". If the latter is the case, you do not need a pitch-up attitude, but a zero-pitch attitude.  Also after saying there is a pitch-up, it says the pitch-up is "illusion" or the floor is not actually parallel to the line of the fuselage. It is not getting to the crux of the question.

I believe the answer may be option 5:
5. The aircraft changes during flight.
At the beginning of a flight an aircraft is loaded with fuel. This increases the weight of the aircraft and thus requires an increase in the AoA to maintain level flight. As the aircraft burns fuel the mass of the aircraft decreases and consequently the AoA must decrease also.
Depending on the aircraft type and the length of the flight, the weight of the fuel can be very significant. For example, a Boeing 777-200 has a maximum fuel capacity of 117,340 lts. This ammount of fuel weighs aprox. 95,000 kg. The maximum take off weight for this type of aircraft is slightly over 247,000 kg. This means that a 777 fully loaded with fuel and with maximum take off weight will lose a bit less than 40% of its mass during flight.

Passenger comfort is a large consideration!  It's simply more comfortable for passengers to be reclined by a degree or two than to sit exactly level.
I have hopped off a 777 onto a small a/c (if I recall correctly, a Baron of some sort) to island hop and the fuselage was pretty much level.  It certainly felt less comfortable and somehow, even as if it was fighting not to descend.  I would prefer to be a little inclined.
I believe that some aircraft cruise slightly nose down.
[EDIT]
CAVEAT.  I am not an expert in physiology or aircraft design.
Comfort is a big factor and the question is not "do airliners fly pitch up" but "why do they?"  That they do is a fact.  I suspect that there are many factors, e.g. the fuselage itself, when pitched up, will generate some lift but ask any experienced flyer about sitting in a rearwards facing seat, or walking towards the front when in a descent which results in a level pitch or pitch down attitude.  It feels less comfortable than when nose up.
If the aircraft is level, and you are level, you experience +1g vertically and 0g horizontally. If you recline the seat, you still experience +1 and 0.  If the aircraft is pitch up, you experience a small -ve g component in the horizontal.  Quite what effect this has psychologically, I don't know but it does make a difference.  I've heard, anecdotally, that facing backwards, e.g. in a British Airways biz class seat is less comfortable than in a forward facing one for exactly this reason.

If a couple of degrees of recline made a genuine difference to passengers, wouldn't it be easier to just tilt the seats backwards a little more? Also, note that your seat probably reclines by more than two degrees just from the pressure of you leaning back on it: it's hard to imagine that this is a noticeable difference.

@DavidRicherby could be a factor, I remember flying in an R22 it was slightly uncomfortable to have the seat tilted forward all the time...

i think during cruising, when the announcement is made that you can walk about and go toilet, or have your meals, definitely the airplane has to be horizontal, otherwise u will not feel balance walking about, or the water level on your cup tilting etc.   but yes, aerodymically the pitch up is to produce the upward reaction force to balance the downward weight of the aircraft.   Simple newtonian calculation.

@DavidRicherby  I've edited my answer.

I don't think passenger comfort plays any role at all. Passengers will get used to however it works.

@Peter.  The pitch up has nothing to do with Newtonian physics or countering the weight.  Lift counters weight and it is possible to generate lift with the nose down, level or up.  In cruise many large type DO fly nose up.  Just a degree or two and, if you could place your water cup level, you would be able to see this slight attitude.  Try placing a marble on the cabin floor in cruise.  It will roll backwards.  Surely there is a real big iron driver here who can confirm that the AI shows nose up in climb?

Of course, that last word should have been "cruise" ;)

Lift can be generated with nose down, but it does happen to be less efficient. Passenger comfort is not relevant. It might be more comfortable, but the designers were not thinking about that. Passengers will not stop flying because the floor is tilted slightly forward and it feels weird. They'll get used to it. But drag affects running cost and saving a percent makes big difference to airlines. So designers design for efficiency, not comfort.

@Jan.  Agreed, but 0 pitch is generally also not fuel efficient since the fuselage generates some lift and also reduces parasitic drag.

@PeterTeoh It's perfectly possible to walk around on a steep hill. Here, we're talking about a very gentle hill -- so gentle that people are disputing whether you'd notice it at all. Also, if pitching up the nose by a couple of degrees produces enough lift to counter the weight of the aircraft, I guess the wings must just be there to hold fuel or something.

@Simon:  "Nothing to do with Newtonian Physics"?   You just commented you are not an expert in aircraft design, so definitely you are not serious with the above statement.   I am a Physics major, and hydrodynamics/aerodynamics/complex analysis are all my modules.   In all these we calculate even the shape and contour of the wing, and not just the tilt.

@David Definitely if it is 1 degree or 2, no problem with walking about, but definitely not more than that, as in the case of initial climbing - which is why you are asked to be seated and belted up, even though there is no turbulence, but steepness of the climb requires that.   But for the slight degree of tilting up, especially for large aircraft, it is necessary, because the weight is so heavy, that you cannot stay horizontal.   Read what the aerospace engineer has to say:
http://sg.answers.yahoo.com/question/index?qid=20110821181822AA10BYO

@PeterTeoh  Of course Newtonian physics describes how lift counters weight.  My point is that the pitch up of the aircraft in cruise has nothing to do with it.  I can set the incidence angle of the wings to the fuselage to give me any deck pitch I want, of course, within reason.  The pitch being discussed is a specific question of why the designers chose a pitch up deck in cruise.  That this is a design choice, and not because it is necessary to generate lift, is without question.

The reason the airplane at cruise is flying nose up at about 2 to 3 degrees (.78 mach and varies only about 1 degree at that alpha, altitude, and speed as a function of weight) has only to do with managing takeoff pitching moments due to engine thrust, requirement to align engines with local flow, and heavy nature of long landing gear structure.  To expand a bit:
1). The engines' thrust has to be horizontal during takeoff so that they don't affect pitch rotation for takeoff.  This could be particularly relevant for engine failure scenarios as this would cause thrust induced rolls and/or variation to pitch response.
2). The engines must be mounted on the wing pods at a specific thrust angle to ensure they align with the local airflow during cruise.  Notice the odd angle MD-88 engines have on the fuselage to align them with the downwash from the main wing.
3) And finally, designers could rotate the wing-engine assembly on the fuselage increasing the wing's incidence to level the fuselage in cruise, but to ensure engines are horizontal on takeoff, the main landing gear extra long to orient the fuselage slightly nose down while on the runway.  Long gear is heavy.
The minor drag increase from a 3º attitude in cruise easy to select to avoid carrying around heavy landing gear.  In fact, the sweep up of B-737 tailcones, A320 tailbones, and nose droop of B757, A320 nose cones removes some of the drag penalty of a nose up fuselage cruise attitude.

Don't know how but I stumbled upon this interesting question which has generated some quite elaborated answers.
For a conventional jetliner, the angle at which the wing is attached to the fuselage is simply chosen so that the total drag of the airplane is minimised during cruise condition. And the total drag at cruise is minimised when the fuselage pitches up a couple of degrees. That's all.
Obviously also the confort of the flight crew pushing food carts in the aisle plays an important role during design phase.


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Aviation ebook for beginners?
I'm new to aviation but I am very passionate about it. I'm just 14 years old, so please help me in finding a good e-book about aviation for free.
I don't know how to search with Google about it.

"A book about aviation" is an entirely too broad topic.  If you have a specific interest within aviation that you are looking for a book about, that would be a better question.  As worded, thousands of books could be suggested to you and none of them may be helpful to you nor people that show up from google.  With that said, welcome to Aviation.SE!  You can take a look at the help center: http://aviation.stackexchange.com/help to get a better idea of what type of questions are appropriate for this site.  Welcome!

Although this is a question based on opinion, it might perhaps have some value as a community wiki so I've marked this 'answer' as such. I also borrowed one of Manfred's links. Feel free to append stuff to the list.

In terms of free download, I can definitely recommend the FAA Airplane Flying Handbook which can be found on the FAA web site. There are also a number of other handbooks there which are great reads. To be honest, I find this the best introductory book I know, free or otherwise.
If you're out for a good reference book, something like Anderson's Introduction to Flight will be good, but bear in mind this is hardly an easy read but does cover virtually everything you will need to know. An older edition seems to be available online.

In terms of the FAA stuff I would go even further: The FAA has a pretty comprehensive series of handbooks on pretty much every aviation topic you can think of, all available as PDFs.

@voretaq7 that's what I was referring to by "a number of other handbooks", but feel free to update the post and append the link. :)

Aviation is a pretty complicated topic and can get very overwhelming very quickly, so it's not easy to locate something specifically.
eBooks however are not too easy to find, since you'll get the full load of manuals and regulatory documents in the search. You might find something (including the ordinary print books below) by searching for book_name filetype:pdf in google.

If you're out for a good reference book, something like Anderson's Introduction to Flight will be good, but bear in mind this is hardly an easy read but does cover virtually everything you will need to know. An older edition seems to be available online.
There are plenty of books on flight simulation, which is often a great place to start. A fantastic one I picked up with lots of facts and stuff was Flight Simulator X for Pilots written by Van West and Lane-Cummings. This covers everything from navigations, maps and handling the aircraft. There are a lot of similar stuff on websites and youtube as well.
There are plenty of websites on model aircraft building and drones. Less theory and more practise, but anyway interesting and educational.
There are plenty of pilot blogs around, where you can read lots of good stuff.

I could also suggest that you join the edX free online course given by Delft University of Technology in Aeronautical Engineering. You get a certificate at the end as well if I'm not wrong, and it should give you a decent introduction if you're able to keep up with it :) Top 20 technical university and the largest faculty in Europe.

Sporty's ground school course is pretty helpful, you can get it for free if you can get yourself on an EAA Young Eagles flight.
I am not sure about ebooks, but you can find copies of these books on eBay or Amazon.

As the Pro Flies (John R. Hoyt)
Stick and Rudder (Wolfgang Langewiesche)

General interesting aviation books

Janes All the World's Aircraft
Janes Aircraft Recognition Guide
A Field Guide to Airplanes, Third Edition (M. R. Montgomery)


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Is there any reason for why the cabin temperature would suddenly become very high?
I was flying a Fokker 100 a few months back over central Europe. We had probably just reached cruising altitude when the cabin temperature suddenly skyrocketed without reason, with the air coming out probably around 30 degrees (Celsius). After complaints by fellow travellers it became cooler. Is there any reason why it would do this?
I guess the pilots might have done it, but I see no reason for it, so could the aircraft have done it on its own accord?

Your flight attendant probably got cold and turned up the temperature until people complained.

@casey maybe it could be so simple. just seemed like the temperature was maxed out however. felt really strange....

@Manfred It's definitely not unknown to happen, it happened on Scandinavian Airlines Flight 751, but that was on the ground, not in the air...

@casey: Sounds like me at some of the places I've lived!

Over Central Europe in the winter time, air becomes tremendously cold. Since warm bleed air from the compressor stage of a jet engine is used for cabin heating, the pilots might have set temperatures to maximum in order to warm the cabin.
But being in a climb, almost all power of the engines is required for lifting the aircraft, thus leaving only little excess bleed air to be used for heating. During normal days and outside air temperatures this should be enough, though.
By levelling out the aircraft, the engines are spooled back (less power required than in climb -> hence more excess bleed air available -> higher ability to warm the cabin in cruise than in climb). If the pilots/cabin attendants just didn't realize this circumstance rapidly enough, the cabin is being flooded with maximum heating air from the engines.

That makes perfect sense. The F70/F100 climate system is extremely sensitive to engine settings I've noticed on several flights.

I've never flown a Fokker, but every jet that I've ever flown produces more bleed air at higher power settings.  The amount of bleed air produced is relative to how fast the engine/compressor is turning.

In addition, some engines have multiple bleed air taps at different stages of the N2 compressor, and engine setting may change which bleed source is being used to supply the packs.

Yet another additional factor is adiabatic expansion of the cabin air.  On climb out the cabin altitude approaches 8000 feet (lower in some airplanes) and for dry air this expansion alone would result in 24C cooling of the air from sea level.  You probably wouldn't notice anything that dramatic depending on residence time of cabin air, humidity and the temperature of the incoming air, but it is something, at least in part, to overcome during the climb.  Once the cabin altitude is stable, you lose this effect and if you the now unneeded heat input may start to warm the cabin.

Bleed air from the engines is mixed with cold ram air (-50°C) from the atmosphere, in a variable ratio, according to wikipedia and the temperature is controlled when pressure varies. How to explain such temperature increase when the aircraft levels off?


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Is it possible and effective to perform a forward slip in a large commercial jet?
I'm wondering if it's possible to forward slip a large commercial aircraft, like the A320 or even B777, and if so:  is effective or useful, since most small aircraft which I gather do it have no spoilers for instance which large aircraft do?

It's it possible?  Yes, you would do it the same way as in any other airplane.
Is it effective?  Yes, just look at all of the fuselage area that is exposed to the relative wind.
Is it useful?  Not really.  With all of the other drag devices, you shouldn't really need it.
Is it recommended?  You would have to check the AFM.  I looked in the A320 Flight Crew Training Manual and there is no limitation against it, but if you need to slip then that's a strong indication of poor planning and an unstabilized approach which would require a go around.  Even at higher altitudes, it isn't very comfortable for the passengers!

Its useful if you're heading into Gimli hot, high, and dry :)

@roe i'm not sure he had the hydraulics to get the spoilers out though with two engines out....

@roe In a "glider" like that, all bets are off and you do what you have to do whether or not it is stabilized or is an approved maneuver!

One of my friends was a heavy pilot for USAFA and during his first flight for the airlines in a 737 he forgot he had 100s of passengers and almost did a slip out of habit!  On a similar note, I would have to disagree, because it is very useful to the air force with large cargo jets, potentially carrying much more than a commercial plane.

It’s been done before by a large craft with engine trouble, a 767 operating Air Canada flight 143. During the change over from imperial to metric there was a flub on calculating the amount of fuel in the tanks of the craft by the ground and cockpit. A tagged out digital fuel gage was the perfect setup for running out of fuel. The captain was an experienced glider pilot and knew how to slip an aircraft and even though it was risky to punish the frame of the aircraft there was little choice. They were able to land safely minus only the front gear on a old airport turned into a drag strip.

My first thought when i saw this question title was "Gimli Glider."

Captain Pearson saved the day on that flight with a forward slip. https://en.wikipedia.org/wiki/Gimli_Glider


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How do KFm step airfoils work?
I was looking for airfoils, and I came across an interesting design. It's called a KFm1 step airfoil. Those of you in model aircraft design might have heard of it. However, I've never really seen one of these in normal aviation.
My questions are:

Why don't they work for full sized aircraft?
Is there some way to make them work?
What gives this airfoil its properties?

From Wikipedia article you linked: "Poor lift-to-drag ratio performance in wind tunnel testing has meant that to date the KF airfoil has not been used on any full size aircraft." Are you asking why they have a poor L/D?

Questions 1 & 2 are answered by the Wiki article, as pointed out. Question 3, however, seems to be a reasonable one to look for an answer to.

@Ron Beyer Partly I'm asking why L/d is so poor, part of the question is whether modifying a different airfoil with a KFm step will also cause low l/d

Related: https://aviation.stackexchange.com/questions/35063/can-a-kline-fogleman-airfoil-be-used-for-engine-turbines

The idea works but only with active automated re-configuration of the
  shape of the step(s) during flight. Further testing has shown that
  this airfoil is effective in low Reynolds number flow.

source: Wikipedia
The Reynolds number is indicative of the speed of the airflow over the wing. The higher the speed, the higher the Reynolds number and vice versa. This is why they would be more suited for model aircraft rather than large aircraft which would experience higher Reynolds numbers.


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How does the CFM LEAP-1B engine achieve the same efficiency as the LEAP-1A despite its lower bypass ratio?
The CFM LEAP engine comes in 3 variants (1A, 1B, 1C). The larger LEAP-1A and LEAP-1C variants have bypass ratios of 11:1, while the smaller LEAP-1B only has a bypass ratio of 9:1.  For turbofan engines, we know that the higher the bypass ratio, the higher the propulsive efficiency of the engine, which results in a lower fuel consumption.
So how does the CFM LEAP-1B engine achieve similar efficiencies to its larger siblings when its bypass ratio is considerably lower?

In addtition to the previous answer...
Higher BPR means larger fan and lower RPM.
But in the LEAP familly the fan and booster (LP compressor) are on the same shaft driven by the LP turbine. And the booster optimal RPM is higher than the optimal fan RPM. The smaller LEAP-1B fan has a higher fan RPM which helps to increase the compressor efficency.
To increase even more the BPR without loss of compression efficency the fan and booster RPM must differ, which can be obtained using a 3rd shaft (Trent familly) or a gearbox PW1100G.


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MH370 blackbox - is it still possible to retrieve data from it?
If the blackbox of MH370 were to be found today, would it actually still provide any information, assuming that it was in 5km deep water or so for some 5 years now?
If not, why would you still be looking for the missing aircraft and especially the blackbox, if there was nothing to find out about the reason that caused the 777 to disappear?

Note that the depth of the ocean is very, very variable. If can change from over 7000 meters to less than 2000 in just 100 km, so the actual depth (and pressure the black boxes have been subjected to) is quite unknown. Also, flight data recorders are designed to withstand quite extreme conditions, both at the time of impact (3400 g!) and after impact. You can find datasheets for some listing 20000ft max depth... There's a reason the black boxes are so big compared to the small SSD they contain....

@jcaron They use SSDs? I was under the impression, especially from this, that black boxes used their own purpose-specific data storage technology.

@JoL I’m not saying they are using off-they-shelf consumer-grade SSDs. But nowadays they are using solid state drives, as opposed to the magnetic stuff with moving parts they used previously. And this kind of storage is definitely very small compared to the overall FDR size. Note however that in the case of AF447, the storage was actually found separate from rhe FDR and was still functional.

@jcaron are you saying the FDR disassembled itself? Or are you saying they found a QAR?

@Harper: He's saying that the FDR's memory module separated from the chassis upon impact, and the two were recovered separately.

There are precedents: the flight recorders of AF447 spent two years at the bottom of the ocean, and revealed all that had happened after being retrieved. So they had survived being immersed in salty water at high pressure, making it very likely that MH370s boxes have survived as well.
Time of immersion is less relevant: oxidation (rust forming) is much slower at greater depth, due to much less dissolved oxygen and lower temperatures. The corrosion that does take place is mainly anaerobic, through bacterial sulfide formation. As posted in for instance this link.

For reference, AF447 was found at a depth of 3980 meters.

+1 for chemistry

If not, why would you still be looking for the missing aircraft and especially the blackbox, if there was nothing to find out about the reason that caused the 777 to disappear?

In fact we are concerned with 2 black boxes, the flight parameters box, and the voice recorder, these are complementary.
The voice recorder is extremely important too, for instance in the Ethiopian 737 MAX, the voice box recorded the repetitive action of the pilots searching for an adequate procedure in the paper checklist
But not only
When a crash occurs, the debris, and every part of the aircraft is capable to talk.  For instance it will tell if the crash occurred while trying a ditching (water landing) or not - such as falling like a stone due to a stall.
But also
Families are concerned, people are concerned, memories are concerned. Don’t be just materialistic, finding the aircraft will help these families to mourn their beloved parent.....

AF447 is also another good example of why the voice recorder is so important. Without the voice recorder, we wouldn't have had nearly as complete of an understanding of how on Earth they crashed an A330 from 40,000 ft to ocean surface.

@reirab:  In contrast, the MH370 CVR, if it's ever found, might not tell us much of anything interesting.  It only keeps two hours of recordings, and it seems plausible that most or all of the crew and passengers were incapacitated for more than two hours before the plane finally crashed.

@MichaelSeifert It's possible, but not necessarily likely. At any rate, it would tell us if that's the case (if you could hear flight noise, but no humans,) which would itself go a long way toward answering questions. You would also be be able to hear automated callouts (or the lack thereof) which could provide useful information. For example, in the AF447 case, hearing the timing of automated callouts and how the crew reacted (or failed to react) to them provided useful information, but they could give us useful information about the aircraft's state even if there were no human voices.

@Michael Seifert, « it seem plausible »! That’s not 100%. But also, May be the recorder lost its supply so many hours ahead of the crash. May be it remained running and recorded nothing in the cockpit. May be some passengers were not incapacitated. If I follow your reasoning ones you make an assumption you stop looking to other colleagues assumptions, and you stop looking for a material proof. If I translate this medically, if you have a health problem and your doctor instead of following a protocol to find the trouble, he relies on a single assumption, would you be satisfied.

Actually, most doctors do follow a memorized or looked up decision tree to diagnose and treat instead of actually thinking about how things work.  If they don’t make a mistake or remember it wrong, this is right for most patients, but the occasional rare case is harmed.

To be clear, I'm not saying that investigators should abandon their search for the CVR — just that I wouldn't be surprised if it didn't help us solve the mystery.


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Is it allowed and safe to carry a passenger / non-pilot in the front seat of a small general aviation airplane?
Is there anything wrong with taking a friend in the copilot's seat of a small general aviation aircraft with me flying, or does he have to sit in the back (if there is one)?

You can even let them fly: Are pilots allowed to let passengers fly the plane?

Most GA planes don't require copilots. so it's not "the copilot's seat".  Some (e.g. C-150/152) don't even have more than two seats.  It's absolutely normal for a passenger to ride in the front.  Indeed, with some (the Piper Cub, for instance) the pilot rides in the rear seat.

In some there is no choice.

On your lap?  Might be awkward and uncomfortable, but probably not forbidden.

@Roger I very strongly suspect that to fall under any "careless or reckless" catch-all, unless a more specific regulation exists in OP's jurisdiction which would cover it. It'd be the kind of thing that maybe, just possibly you could get away with as long as nothing goes wrong (because it could be made unlikely that someone would find out), but if something does go wrong, such a regulation would certainly be used against the pilot by the authorities.

There should be no problem in general with flying with a passenger in a front row seat in a GA flight, as long as the aircraft is certified for single-pilot operations. You'd want to check your national regulations to be certain, but I have a hard time imagining that it would be prohibited as long as you're allowed to carry passengers in the first place. In general, it's normal practice in small airplanes for passengers to fly up front.
However, especially for anyone not used to a cockpit environment, you would definitely want to brief them on expected behavior before beginning the flight, in addition to any pre-flight briefing required by legislation. Even if such legislation only require briefing before a commercial flight, it might be good, and put your passenger more at ease, to do something similar before a non-commercial flight as well. (How to get out of the seat belt, how to exit the aircraft, where the airsickness bag is, ...)
None of this needs to be complex stuff; what I have in mind here is mostly things like keep your feet clear of the pedals, keep your legs clear of the yoke, don't touch any of the controls unless told to, and similar. As Jamiec points out in their answer, it's very unlikely that someone not used to light aircraft would know what the rows of instruments, switches and controls are about, so a quick "fly safely in the cockpit" style briefing would absolutely be appropriate in addition to a general pre-flight briefing.
For a (somewhat humorous) example of what I have in mind, you might want to check out Preflight Announcement, Maule on Youtube.
Especially since this is someone you know, and you'd therefore presumably be able to gauge their reactions more easily than if they were a stranger, don't be afraid to sprinkle some appropriate humor into the briefing. For one example, I've heard of the airsickness bag being referred to as the rollercoaster bag.
It may also help put your passenger at ease if you specifically tell them what you're about to do before you do something unusual or non-obvious, such as the engine runup and magneto check. Particularly with non-pilot passengers, you don't want to get technical; something like "I'll do a few engine tests to make sure it's running smoothly before we take off" is more meaningful to them than "I'll bring the engine to 2391 RPM while holding position, and then check the magnetos and carb heat before reporting ready to Tower". Certainly when flying with another pilot you might just say "mag check", or even nothing at all (they'd probably be expecting you to do it).
Especially if your friend is an adult or an able teenager (but probably not for people much younger than that), do consider the possibility of enlisting their help with simple tasks during the flight. Regulations permitting and of course assuming that you as the pilot in command feel comfortable with it, you could even let your friend take the controls for a while, as long as you're able to take over if necessary and you're able to ensure that nothing untoward happens. If nothing else, they can definitely help look out for and call out nearby traffic while hopefully enjoying the view.
You could also show your friend how to use the radio to contact ATC in an emergency, and at least the very basics of keeping the airplane in the air (things like mostly straight and level flight; shallow turns, possibly without rudder; climb and descent; stall indication and response; where the throttle is and how to operate it; and possibly the IDENT function on the transponder). In the unlikely event that something were to happen to you, while not a guarantee, doing so would greatly increase the odds of both of you eventually making it out of the airplane in one piece. I have written a much more in-depth answer about this from the passenger's perspective which you might find informative. It's possible that there are even courses specifically tailored toward GA passengers in your locale, which would/could cover such topics; if not, any instructor worth their salt should be able to put something together easily enough for a given airplane type. If this is someone you expect to fly with often, that might be money well spent for both of you.

I'm not a pilot, but personally, I'd also explain to people of that last category (adults and able teenagers) how to operate the radio so at the very least, if something happens to me while I'm flying, they can contact Traffic Control and get advice. That is assuming whatever might have happened to me doesn't interfere with the controls of the plane.

@Nzall That's a good idea. I've added it to the answer.

Yes, friends & family can sit up front with you in a light aircraft.
It is your responsibility as PIC to brief the passenger regarding the controls - which anyone not used to a light aircraft may not be familiar with - the last thing you want  is them pushing the yoke forward at the wrong time.

Even worse is when they get "scared" and push their feet against the pedals. Some people don't understand that it isn't a "brake and a gas" and may push one or both. Nothing more fun than landing with a nervous passenger holding your brakes locked.

@RonBeyer : That's a similar problem with trainees at the beginning. My instructor nearly crashed with a fellow trainee on their first flight as the trainee got panicked, grabbed the yoke and instinctively pulled it to himself. The two yokes were mechanically coupled, and thankfully the instructor was physically much stronger so he could wrestle it free before they would have stalled.


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What terminologies are used when ATC instructs a pilot to stop or proceed with his transmission?
If some pilot forgets to release his mic button, distracting everyone on the frequency, what terminology can be used by an ATC to stop it?
And if another pilot stop transmitting his message until the former pilot release his mic button, what terminology can be used by an ATC to make him resume and finish his transmission?

If a pilot forgets to release his mic button, you can't talk to him. VHF radio is simplex, so only one station can transmit at the time. If more than one station transmits at the same time, the signal will sound garbled. As a result, there is no standard phraseology to use in such a situation. All you can do is wait for the pilot to discover the issue. See this question for additional info.
CPDLC (text based communication between ATC and the cockpit) does have a "CHECK STUCK MIC" message that can be sent to aircraft on a frequency with a stuck mic. But CPDLC is not globally available, and only used in the en-route environment.
When someone is waiting to transmit, ATC will use the phrase "Go ahead" to indicate that they can start their call. This will not be very useful in the case of a stuck mic, for the reason described above, but the "Go ahead" phrase is often used in other cases where ATC has told a pilot to wait ("Standby"), typically because ATC is busy on the phone or another, more important radio call has to be made first.

OK but is there some protocol for this?  Like switching to another frequency?

@JoelFan Have a look at the linked question that covers this issue more specifically